The present invention relates to a receptor layer transfer sheet (intermediate transfer medium film) usable for transferring a receptor layer, on which an image has been preliminarily formed, to a surface of a transfer-receiving material and also relates to a card-shaped printed product prepared by using such receptor layer transfer sheet.
There have been known thermal transfer methods as image formation method. In such methods, a thermal transfer sheet, composed of a substrate sheet and a coloring material layer formed on the substrate sheet, and a transfer-receiving material on which a receptor layer is formed as occasion demands, are disposed and pressed between a heating device such as thermal head and a platen roll, and heating portions of the heating device are selectively heated in accordance with information of images to be transferred, so that a coloring material contained in the coloring material layer on the thermal transfer sheet is transferred on the transfer-receiving material thereby to record the images thereon. These thermal transfer methods are generally classified into a fusion thermal transfer method and a sublimation transfer method.
In these thermal transfer methods, the fusion thermal transfer method is a method in which a thermal transfer sheet carrying a heat fusible ink layer is heated by the heating means of the type mentioned above and a softened heat fusible ink is transferred on a transfer-receiving material such as natural fiber paper or plastic sheet thereby to form an image on the transfer-receiving material. The heat fusible ink layer used in this method will be prepared by dispersing a coloring material such as pigment into a binder such as heat fusible wax or resin, and the heat fusible ink layer is carried by a substrate sheet such as plastic film. An image formed by this fusion thermal transfer method has an improved high density and sharpness, and hence, this method is more applicable to the recording of binary images such as letters or lines. Colored or multiple-colored images can be formed by using a thermal transfer sheet provided with heat fusible ink layers of yellow, magenta, cyan, black and the like and recording them on the transfer-receiving material.
On the other hand, the sublimation thermal transfer method is a method in which a thermal transfer sheet carrying a sublimation dye layer is heated by the heating means of the type mentioned above so as to sublimate the sublimation dye contained in the dye layer, and the dye is then transferred on a receptor layer formed on the transfer-receiving material, thus forming an image. The sublimation dye layer used in this method will be prepared by dissolving or dispersing the sublimation dye as coloring material into a binder such as resin, and the sublimation dye layer is carried by a substrate sheet such as plastic film. According to such sublimation thermal transfer method, since transferring amount of the dye can be controlled in dot unit in accordance with energy amount of the heating device such as thermal head, a gradation reproduction due to density modulation can be made possible. Furthermore, since the dye material is used as coloring material, the thus formed image has a transparency, and hence, this method is superior to the reproduction of intermediate colors at a time when a plurality of dye layers of a plurality of colors are transferred in an overlapped manner. For this reason, a full-colored image with high quality can be formed by transferring the sublimation dye of three or four colors of yellow, magenta and cyan, in addition to black, on the transfer-receiving material in an overlapped manner by using the thermal transfer sheet provided with sublimating dye layers of these three or four colors.
In these image forming methods, it is necessary particularly for the sublimation thermal transfer method that the transfer-receiving material on which an image is to be formed is provided with a dyeing property of the dye. Because of this reason, in a case where the surface of the transfer-receiving material has a less dyeing property, it is almost difficult to form an image on the transfer-receiving material as far as the receptor layer is provided thereon.
For example, the Japanese Patent Laid-open Publication No. SHO 62-264994 discloses a technique for providing a receptor layer on a transfer-receiving material having no dyeing property in a manner that a receptor layer transfer sheet formed by providing the receptor layer on a substrate film to be separable is preliminarily prepared and this receptor layer is transferred on the transfer-receiving material. According to this technique, a dye is transferred from a dye layer of a thermal transfer sheet to the receptor layer already transferred on the transfer-receiving material to thereby form an image.
Furthermore, in the Japanese patent Laid-open Publication No. SHO 62-238791, there is disclosed a technique such that a receptor layer transfer sheet formed by providing the receptor layer on a substrate film to be separable is preliminarily prepared and an image is formed by transferring a dye from a thermal transfer sheet on this receptor layer. Thereafter, the receptor layer bearing the image is transferred to the transfer-receiving material by heating the thus formed receptor layer transfer sheet.
Still furthermore, in the Japanese Patent Laid-open Publication HEI 7-156532, there is provided a transfer sheet, on which a receptor layer having an improved image and texture(or feeling) is formed by controlling surface roughness of the receptor layer transfer sheet.
According to these conventional methods or techniques, it becomes possible to transfer and form images on transfer-receiving materials such as a material having a good dyeing property such as card made of polyvinyl chloride, a material having a poor dyeing property or a material, such as polycarbonate resin, easily fusible by the heating of the thermal head.
Still furthermore, in order to obtain an improved durability of images formed by the fusion thermal transfer method or the sublimation thermal transfer method, the Japanese Patent Laid-open Publication No. HEI 3-45391 discloses a technique such that an ionizing radiation hardening resin layer provided with an adhesion layer as an image protection layer is formed on the image through the thermal transfer process to improve the durability of the image.
There have been further provided other methods for improving weather-proof property by forming a ultraviolet shut-off layer by a method similar to that mentioned above.
However, for card-shaped printed products such as ID (identification) cards, it is particularly important to have an improved durability, and many attempts have been made for achieving such purpose. Furthermore, in the conventional protection layer formation methods, the protection layer has been formed by transferring the protection layer on a transfer-receiving material, on which the image had already been transferred and formed, from a protection layer transfer sheet which had been prepared separately. Accordingly, the preparation of the card-shaped printed product having the improved durability by the protection layer has been complicated.
Furthermore, in a case where an image is transferred and formed by the receptor layer transfer sheet on the transfer-receiving material having a poor dyeing property, it has been required to further transfer the protection layer from the protection layer transfer sheet. Accordingly, in such case, the preparation of the card-shaped printed product formed of a material having a poor dyeing property has been also complicated to improve the durability of the image.